1. Field of the Invention
The invention relates to an image forming apparatus such as a copier, printer or facsimile machine employing a toner to form images. In particular, the invention relates to transfer technology for transferring a toner image formed on a surface of an image carrier (a photosensitive body etc.) on to a surface of a transfer medium (recording medium etc.).
2. Description of the Related Art
Generally speaking, in an image forming apparatus employing a toner to form images, it is necessary to transfer an image formed on a surface of an image carrier such as a photosensitive drum or the like onto a transfer medium such as a paper.
In order to faithfully transfer an image formed on a surface of an image carrier onto a transfer medium such as a paper so that it will reproduce well, it is necessary to prevent splashing of toner in the vicinity of a transfer portion.
In order to meet this demand with a relatively simple construction, the image forming apparatus of Japanese Patent Publication Hei. 6-202496, having the transfer structure shown in FIG. 10 has been proposed.
In FIG. 10, the reference numeral 1 indicates an image carrrier member (photosensitive drum), upon the surface of which a toner image is formed. The reference numeral 6 is a transfer medium, and 8 is a transfer medium support.
The refernce numeral 4 is a transfer charging means, comprising a conductive layer 401 made of a conductive rubber which has a shaped of a rectangular plate-like piece elongated in a direction perpendicular to the direction of conveyance of the transfer medium, and a highly conductive electrode 402 bonded to conductive layer 401 by means of a conductive adhesive and capable of applying a uniform current in the direction of thrust with respect to conductive layer 401. An abutting layer 405 having a lower coefficient of friction than that of the conductive layer 401 is provided by coating or the like on an upper surface of the conductive layer 401 contacting the transfer medium support 8. Further, a pushing member 404 (formed of a plate-like or film-like flexible member or the like) is disposed in an opposite side to that in which the abutting layer 405 of conductive layer 401 is arranged with respect to an electrical field applying member comprising the electrode 402, conductive layer 401 and abutting layer 405; and a uniform pushing force suitable for transfer is obtained in a sideways direction.
According to this kind of the image forming apparatus, a latent image is formed on the surface of the image carrying member 1, which rotates in the direction of arrow B in FIG. 10, by means of a laser beam or the like (not shown in the drawing), and this latent image forms a toner image on the surface of the image carrying member 1 by means of being developed by a developing means not shown in the drawing.
The transfer medium 6 is transported by the transfer medium support 8 in the direction of arrow A, and the toner image on the surface of the image carrying member 1 is transferred onto the transfer medium 6 by the application of an electric field by transfer charging means 4 at a transfer portion 3 (the portion contacting image carrier 1).
In the image forming apparatus described above, the shape of transfer charging means 4, positioned further downstream in the direction of conveyance of the transfer medium 6 than the transfer portion 3, is such that it is rectilinear and drops away suddenly due to the upper surface 4a and side surface 4b. Because of this, the electrical field positioned-downstream of the transfer portion changes suddenly, static electrical discharge occurs easily, and toner splash (especially splashing of the toner after transfer to the transfer medium 6) is created, and as a result, the problem arises that there is a fear that it will not be possible to carry out faithful transfer of a toner image which can be reproduced well onto the transfer medium.